versstef1 said:
Two things. 1. How do you determine "actual PPM" for a given FC/CYA ratio? I tested my tap water last night and it had about 2-3 PPM, which seems really high. According to the county water test report, this is supposed to be around 1 PPM. Either way, how do I get the equivalent number for my pool?
2. Not sure I can make this distinction really well, but the question we still have is this: Just because the chlorine is "bound up" in the CYA, that doesn't mean it's not in the water, right? So there would still be absorption of it into the skin at all times, regardless of what the "active" or "actual" FC level might be? And what about the stabilizer itself, couldn't that in theory be considered a harmful chemical in its own right? This is regardless of felt or smelled impressions - it's still in the water, no and thus in the skin, no?
It's not like we will stop swimming, but understanding this does seem to make a difference in whether we consider the pool something hazardous that should at least be minimized or something entirely benign that can be enjoyed for hours on end. I mean, it's certainly not as healthy as an alpine mountain stream, so where does it fall on the health hazard scale?
There is no CYA in tap water so the FC that you measure is all unbound. The portion of it that is active chlorine (hypochlorous acid) from a disinfection point of view is a function of pH where it's about half at a 7.5 pH. From an oxidizing point of view, both hypochlorous acid and hypochlorite ion participate in those reactions; which one participates depends on the chemical it is reacting with. The
2012 Orlando Utilities Commission (OUC) Water Quality Report shows chlorine ranging from 0.20 to 2.09 with an average of 1.04. When you say "2-3 PPM" it sounds like you aren't using a FAS-DPD chlorine test kit where you would be able to measure within 0.2 ppm using a 25 ml sample. If you are using test strips, then your measurements are not likely to be accurate.
The active chlorine level for your pool can be roughly estimated by the FC/CYA ratio (technical derivation of why this works is in
this post). The minimum FC for the CYA level in the
Chlorine / CYA Chart is around 7.5% so the active chlorine level is roughly equivalent to water with an FC of 0.075 with no CYA (the actual number for FC equivalence is temperature dependent varying from 0.062 at 77ºF to 0.161 at 90ºF). This is over 10 times lower in active chlorine level than even 1 ppm FC tap water. The rate of oxidation of swimsuits, skin and hair will be 10 times slower as a result.
The reactivity of chlorine bound to CYA is essentially negligible for the CYA levels we recommend (i.e. 80 ppm or lower) since it's roughly 200 times slower to disinfect and oxidize. Even accounting for there being more chlorine bound to the CYA, it still works out as something we can ignore. With an FC of 5 ppm with CYA of 50 ppm, for example, the unbound chlorine is like 5/50 = 0.1 while the bound chlorine is like 5/200 = 0.025. The chlorine bound to CYA as well as CYA itself has essentially no dermal absorption (the dominant species is negatively charged and the neutral species are relatively bulky compared to normally transported small ions and molecules -- see
this link and
this PDF file showing absorption at 5 µg/kg/day).
The primary hazards from chlorine are in the irritating disinfection by-products in the short-term such as nitrogen trichloride that can be inhaled and with disinfection by-products with long-term potential consequences for cancer such as the brominated trihalomethanes (THMs) that are both absorbed through the skin and inhaled. Because of the low active chlorine level, the rate of disinfection by-product production is lower on skin while in the bulk water its rates depends on the buildup of chemicals to oxidize that form THMs which is relatively low due to low bather load. For nitrogen trichloride, the low active chlorine level, the low bather load, outdoor air circulation, and sunlight all keep that chemical to a minimum. Generally speaking, only the indoor high bather-load (typically commercial/public) pools have significant issues with disinfection by-product control, though outdoor high bather-load commercial/public pools would be second in those issues.
During a discussion I had in another forum in response to someone saying chlorine was toxic, chlorine was poison, etc., I was reviewing the hundreds of scientific peer-reviewed papers in respected journals that I had downloaded (and for many, had to pay for) and wanted to summarize them which is, of course, hard to do. I did find the
Environmental Health Criteria 216 "Disinfectants and Disinfectant By-Products" document from the World Health Organization (WHO) from 2000 (updated somewhat in 2004) and thought it would be helpful to quote it's summary info below.
Epidemiological studies have not identified an increased risk of cardiovascular disease associated with chlorinated or chloraminated drinking-water. Studies of other disinfectants have not been conducted.
The epidemiological evidence is insufficient to support a causal relationship between bladder cancer and long-term exposure to chlorinated drinking-water,THMs, chloroform or other THM species. The epidemiological evidence is inconclusive and equivocal for an association between colon cancer and long-term exposure to chlorinated drinking-water, THMs, chloroform or other THM species. The information is insufficient to allow an evaluation of the observed risks for rectal cancer and risks for other cancers observed in single analytical studies.
Studies have considered exposures to chlorinated drinking-water, THMs or THM species and various adverse outcomes of pregnancy. A scientific panel recently convened by the US Environmental Protection Agency reviewed the epidemiological studies and concluded that the results of currently published studies do not provide convincing evidence that chlorinated water or THMs cause adverse pregnancy outcomes.
Now if one looks at the details in the long document, one will find individual epidemiology studies showing links to a variety of cancers and that is what many pseudo-science websites selling products such as water filters or alternative disinfectants all show. However, if you look at the details, you find that nearly every study that shows a correlation has another study that shows no correlation and for many that do show something, the odds ratios are low and all are less than 2 meaning doubled risk. When this sort of mixture of studies happens and where odds ratios are fairly low, it often means that there are confounding variables people aren't taking into account. For example, if you find a correlation of lower cancer risk with people drinking well water compared to chlorinated municipal water, it may be due to well water being in rural areas where more people work on farms or doing heavier labor for more exercise compared to people in cities/suburbs. Unless the study explicitly looks for exercise or physical labor as a variable, they will falsely attribute cancer risk to chlorinated water rather than the lower level of exercise.
The point I'm making is not, by the way, that chlorine disinfection by-products are harmless, but rather that their risk at the levels found especially in low bather-load residential pools is very low. As for alpine mountain streams, if an animal has relieved themselves upstream, I sure as heck wouldn't want to drink that water. All drinking water you buy, including that bottled from alpine mountain streams, is disinfected. See
this CDC link for a sample of pathogens that may be found in untreated water.
